An Introduction to the Avermectins

Abstract
The avermectins are macrocyclic lactones with exceptional potency and spectrum of activity against nematode and arthropod parasites. They are produced by Streptomyces avermitilis. They are active when given orally or parenterally, at dosages of a fraction of a mg per kg, against many immature and mature nematode and arthropod parasites of sheep, cattle, dogs, horses and swine. The avermectins appear to paralyze nematodes and arthropods by potentiating the presynaptic release of .gamma.-aminobutyric acid, blocking post-synaptic transmission of nerve impulses. A chemically modified derivative, 22,23-dihydroavermectin B1, known generically as ivermectin, was selected for development.